Grmoščica

Flora

Trees include Castanea sativa,^[8] Fagus sylvatica,^[8] Quercus petraea,^[8] Salix alba,^[9] S. purpurea,^[10] and others.

There is currently a Robinia pseudoacacia infestation, and foresters are trying to force the growth of native Q. petraea and F. sylvatica to combat it. The local C. sativa population is still badly affected by Cryphonectria parasitica.^[8]

The lichen species found on oak bark on the hill are Flavoparmelia caperata^[11]: 26 and Hypogymnia physodes.^[11][12]

Basidiomycetes include Amanita caesarea, Hygrophorus eburneus, Laeticutis cristata,^[13] Lycoperdon perlatum, Russula cyanoxantha.^[14]: 30

Fauna

Insects include Subcoccinella vigintiquatuorpunctata^[15] and the invasive species Dryocosmus kuriphilus, the latter a risk for the spread of Cryphonectria parasitica.^{[16]: 500 [17]: 162}

Geology

An approximately 20 metres (66 ft) thick open profile of terrestrial non-carbonate loess can be observed in the former clay pit of Grmiščica. These Quaternary deposits were sampled in 2017 and determined to belong to the Bistra unit. They are not separated from the underlying Upper Pliocene strata, which are exposed on the northern flanks of Grmoščica. Fossils of fish and mammals have been found on the southeast flanks of the hill.^[18]

Tectonically, Grmoščica is transected northweast-to-southwest by a relatively lowered block.^[19]

Grmoščica is home to some of the most active landslides in Zagreb.^[20] A large area of the forest on Grmoščica is under private ownership, which has resulted in forest loss, which has led to landslide formation.^[21] The main landslide, the Grmoščica Landslide, spans an area of 2 hectares (4.9 acres), with a depth of 5–9 metres (16–30 ft). The first, partial^[22] stage of landslide remediation was completed at the end of 2007,^[23] in response to some recent wet mass movement.^[24] Some have had to leave their homes because of the landslide even after remediation.^[25][26] The landslide is still active as of 2025.^[27][28]

Speleology

Kustošijanka is a cave with two entrances and 44 m of passageway on the north slope of a valley on the east side of Grmoščica. It is located on the fault line dividing Grmoščica in half from northeast to southwest. Its entrance is at an elevation of 155 m. The caver Darko Višek learned of its existence in conversation with local resident Vlado Krapljan, who was among the visitors who left many names and dates inscribed on the walls of the cave in their childhood. It formed in Upper Pontian layers of marlstone, duststone, and sandstone: "Rhomboidea layers", deposited in brackish conditions.^[29] Thanks to being on a landslide-prone part of the hill,^[30] the entrance became covered at some point after 1993 and could only be passed following digging in 2010.^[31]

Recreation

The arrangement of the Forest Park Grmoščica for recreation has been described as "neglected" by authorities.^{[38][39]: 23} This began to change following the inclusion of the addition of recreational infrastructure to the park plan.^[40] A series of new downhill bicycle routes were added in 2021,^[41] although the majority of routes had been constructed on private initiative.^[42]

One of the earliest and more successful branches of the Croatian Pin Bowling Federation [hr], Grmoščica, founded in 1938,^[43] meets on the hill.^{[44]: 7 [45]: 251} Within Yugoslavia, they won the male national cup 9 times.^[46]

Grmoščica sometimes hosts Mountain biking races, including the Grma mini DH competition in April 2011 won by Berislav Topol,^[47] the Downhill Grma competition in May 2015,^[48][49] an Enduro race in 2021 won by Frano Liović^[50] and an XCO competition in March 2022.^[51]

The view from the top of Grmoščica has been described as "the most beautiful view of Zagreb".^[52]